The present disclosure relates to illumination devices with a light guide and image reading devices with a light guide and particularly relates to a technique in which light having entered the light guide through the incident surface thereof is diffused toward the exit surface of the light guide.
In image reading devices, such as a scanner, image reading is performed by applying light to an original document from which an image is to be read and receiving, at a light-receiving element, reflected light from the original document. In recent years, from the viewpoint of energy saving, downsizing, and so on, there emerge, as illumination devices for applying light to an original document from which an image is to be read, those employing a line light source in which a light source formed of a light-emitting element, such as an LED (light emitting diode), is combined with a light guide configured to guide light emitted from the light source. A plurality of light diffusion patterns are provided in a row on a surface (diffusing surface) of the light guide opposite to an exit surface thereof through which light exits the light guide. The light diffusion patterns are configured to diffuse light having entered the interior of the light guide to allow linear illumination light to exit the light guide toward the original document from which an image is to be read.